1. Technical Field
The present invention relates to liquid ejecting apparatuses including recording heads of, for example, ink jet type, and in particular to a liquid ejecting apparatus including a plurality of liquid ejecting heads.
2. Related Art
Liquid ejecting apparatuses refer to apparatuses including liquid ejecting heads and configured to eject various kinds of liquid from the liquid ejecting heads. An image recording apparatus such as an ink jet recording apparatus (hereinafter simply referred to as a printer) is an exemplary typical liquid ejecting apparatus. The printer includes an ink jet recording head (hereinafter simply referred to as a recording head) functioning as a liquid ejecting head and performs recording by ejecting droplets of ink in a liquid state from the recording head toward an object of ejection, such as recording paper, and causing the droplets to land on the object, thereby forming dots. In recent years, liquid ejecting apparatuses have been applied not only to image recording apparatuses but also to various manufacturing apparatuses such as display manufacturing apparatuses.
The printer includes a recording head (serial head) having a shorter width than a recording medium (object of liquid ejection) such as paper or resin film, a head moving mechanism that moves the recording head back and forth in a head scanning direction, a transportation mechanism that performs sub-scanning by transporting the recording medium in a direction orthogonal to the head scanning direction, and so forth. The printer records an image or the like onto the recording medium by alternately repeating ink ejection from the recording head performed during main scanning and transportation of the recording medium (sub-scanning). In such a method, however, the speed at which the recording head is scanningly moved is limited. Therefore, in a case where, for example, an image is to be recorded on the entirety of a relatively large recording medium, it takes a correspondingly long time to complete the recording.
To solve such a problem, a recently proposed recording apparatus (JP-A-2009-137091) includes a head unit in which a plurality of recording heads are provided in a first direction on a carriage, the recording heads each having a nozzle group including nozzles arranged in a plurality of rows extending in the first direction. The overall first-direction length of the nozzle groups provided in the plurality of recording heads corresponds to the maximum recordable width of a recording medium. The recording apparatus ejects ink while moving the head unit in a second direction crossing (ideally, orthogonal to) the first direction but without moving the head unit in the first direction relative to the recording medium. Such a configuration realizes a shorter recording time than in the case where a serial head is employed.
In the printer that performs recording with a plurality of recording heads, however, the intervals between the recording heads fixed on the carriage may change because of thermal expansion of the recording heads and/or the carriage included in the head unit due to changes in the ambient temperature and/or heat generation from the recording heads. If the temperature inside the printer becomes higher than the ambient temperature obtained during a manufacturing process of attaching the recording heads onto the carriage and the intervals between adjacent ones of the recording heads, for example, recording heads A and B shown in FIG. 6, increase from those determined in the manufacturing process, the positions of the nozzles of the recording heads A and B are shifted relative to each other from those shown by broken lines to those shown in solid lines. Consequently, the landing positions of ink droplets on the recording medium are displaced from the originally expected positions, and the density of dots becomes uneven. Such unevenness in dot density may appear as unwanted lines in the image recorded on the recording medium, deteriorating the quality of recording. Such a problem often occurs when an image is printed in a single color of ink with a plurality of recording heads.